In view of the recent trend to sophistication and miniaturization of machines and equipment in the electric and electronic areas and aircraft and vehicles, a new material which has an excellent heat resistance is demanded. Heretofore, epoxy resins, maleimide resins, and polyimide resins were used in the field where the heat resistance is required. Epoxy resins, however, are not necessarily satisfactory in heat resistance and curing rate, although those have excellent electrical properties. Also, polyimide resins are insoluble and infusible and therefore difficult to mold, although those have an excellent heat resistance.
The polymaleimide represented by N,N'-4,4'-diphenylmethane bismaleimide has a high thermal stability, but has the disadvantage that it has a slow curing rate and requires heating at a high temperature for a long period of time for complete curing. This invention has been attained to improve the curing of polymaleimide.